1. Field of the Invention
The present invention relates to the art of forming magnetic heads for reading and writing information on magnetic recording media. More particularly, the present invention is directed to a method of forming magnetic heads having surface contour designed for reading and writing information on magnetic recording media at high speed.
2. Description of the Prior Art
In recording and playback, a magnetic medium such as magnetic tape moves past a magnetic head, which is formed of at least one electromagnet with a highly focused fringing field. For certain applications, it is desirable to record data onto a tape at a high rate. To accomplish this, the tape speed is increased with increasing data rate.
FIG. 1 shows the region of a magnetic head 10 which is contacted by a magnetic tape 12. Typically, the magnetic head has a convex curve contour at the tape contact region. Nominally, the tape comes into contact with the head at a tangent to the curved head surface as the tape passes over the head. The magnetic head 10 includes a body 13 on which a pair of magnetic pole tips 16 are attached. The tips 16 are exposed at the surface of the magnetic head 10 facing the magnetic tape 12. Between the tips 16 is a gap 18 across which a magnetic field may be created by electromagnetism of a magnetic core (not shown) which is located within the body 13 of the magnetic head 10. The thickness of the tips 16 at the gap, i.e. gap depth 20, is one of the factors which determines the service life of the head. Specifically, the magnetic tape 12 is abrasive to the tips 16. The tape rubs against the tips as the tape passes over the tips. The tips eventually wear out when the gap depth reaches zero at which time the service life of the head ends.
As the tape 12 passes over the tips 16, the tape may separate from the tips 16. Tape separation from the magnetic head arises from, among other phenomena, foil-bearing effect between the tape and the head. Such effect is caused by entrainment of air, by the boundary layer on the side of the tape facing the head, toward the head and between the tape and the head thereby creating an lifting force on the tape. It has been found that the higher the tape speed, the more profound the effect.
Tape separation from the head affects the magnetic field intensity of the tips 16 acting on the magnetic tape 12, which in turn affects the resolution of the data recorded on the tape. Generally, the loss in magnetic field intensity is directly proportional to the separation spacing between the tape and the head and inversely proportional to the wavelength of the recorded signal (or directly proportional to the frequency of the recorded signal). It follows that for high speed recording at high data ate, close tape to head contact should be maintained in order to obtain good data resolution. A close tape to head contact may be obtained by increasing tape pressure on the head so as to overcome tape separation from the head due to the foil-bearing effect. Increasing the tape pressure, however, will increase wear of the tips and consequently shorten head life.
Instead of increasing the tape pressure on the head to overcome the lifting force on the tape, the tape facing head surface may be formed with a modified contour which will reduce the foil-bearing effect. This method is discussed by Abraham Eshel at pages 500 to 503 of FLUID FILM LUBRICATION edited by William A. Gross and published by John Wiley & Sons, Inc. in 1980.
The method includes forming a discontinuity in the curvature of the tape facing head surface at the point where the tape first comes into contact with the head as the tape moves across the head, such as at the point 19 in FIG. 1. Specifically, the contour includes a corner between upstream and adjacent downstream curved surface sections, as referenced to the direction of tape movement. The tape comes into contact with the downstream curved surface section starting at the corner such that the tape is at an angle to the upstream curved surface section at the corner of the curved surface sections. According to Eshel, the foil-bearing effect is reduced in the presence of such discontinuity in head surface curvature.